1. Field of the Invention
The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium (and more particularly to a coating-type magnetic recording medium incorporating a magnetic coating film as a magnetic layer thereof), such as a magnetic tape or a magnetic disc, having a magnetic layer (in particular, a magnetic layer of a type containing magnetic powder and a binder as main components thereof) formed on a non-magnetic support member thereof.
2. Description of the Related Art
In recent years, magnetic recording mediums have been widely employed as recording mediums or storage mediums for audio apparatuses, video apparatuses, computers and the like. The need for the magnetic recording mediums has considerably been raised.
In general, a magnetic recording medium of the foregoing type has a structure that a magnetic layer composed of magnetic powder and a binder is formed on a non-magnetic support member made of polyester film and the like. In general, the magnetic layer is formed by applying or transferring, to the non-magnetic support member, a magnetic coating material, in which magnetic powder is dispersed in a composition containing a binder.
The magnetic layer is formed by, for example, coating a non-magnetic support member made of polyester or polyethylene terephthalate (PET) with a magnetic coating material prepared by dispersing powder of a magnetic alloy or the like, the main component of which is magnetic oxide, such as ferrite or chrome oxide, or Fe, Co or Ni in a binder made of organic polymer material.
The magnetic recording medium manufactured as described above is called a so-called coating type magnetic recording medium, which is required to improve the electromagnetic conversion characteristic thereof.
To realize excellent electromagnetic conversion characteristics of the magnetic recording medium of the foregoing type, enlargement of the output, elimination of noise and improvement of the surface characteristics are required. If the surface characteristics are improved, there arises a problem in that bias noise is intensified.
To prevent bias noise, it might be feasible to employ magnetic powder having a large specific surface area (SSA). In the foregoing case, the size of each of particles is reduced. Thus, the magnetic energy is reduced excessively to maintain a sufficiently high residual magnetic flux density. Therefore, there arises a problem in that reproduction output is reduced.
To prevent reduction in the reproduction output caused from an excessive spacing loss in a short wavelength region, minimization of asperities of the magnetic layer is required. If the surface characteristics are improved excessively, a defects in the movement, such as the foregoing bias noise, TN (Tape Noise) and stick, occur during movement of the tape. Therefore, an optimum coating film is required.
To meet the foregoing requirement, a contrivance has been suggested with which a magnetic layer having a multi-layered structure is employed.
A magnetic recording medium having a structure in which a first magnetic layer and a second magnetic layer are stacked on a non-magnetic support member will now be considered. Changes of the specific surface area of magnetic powder for use in the first magnetic layer and the second magnetic layer, the coercive force of each magnetic layer, the residual magnetic flux density and the film thickness permits satisfactory electromagnetic conversion characteristics to be obtained.
Although the electromagnetic conversion characteristics of the foregoing magnetic recording medium can somewhat be improved, both of satisfactory durability and excellent reliability cannot easily be realized while improved electromagnetic conversion characteristics are being maintained because of limitation of the manufacturing process. To realize satisfactory characteristics, magnetic powder and each magnetic layer must meet furthermore severe requirements.